Arc discharge device



May-3, 1949. c. G. SMITH 2,468,783

ARC DISCHARGE DEVICE Filed April 3, 1946 v 2 Sheets-Sheet 1 a I Luaunaa INVENTOR CHARLES 6. SMITH l ll'hml 'r H m [920;

Patented May 3, 1949 UNITED STATES PATENT OFFICE sac DISCHARGE DEVICE Charles: Smith; Medford,, Mass, assignor to Raytheon. Manufacturing Company, Newton, Mass.,a corporation of Delaware Application- April 3, 1946-, Serial No. 659,228

6. Claims.

This invention relates-to: arc discharge devices of the type employing pool type cathodes, and more: particularly to means for controlling the arc; cathodespot thereon.

Heretofore attempts to control currents by extinction of the arc discharge have required the use of. complicated. and. relatively ineffective devices;

The primary object of the invention is to provide a device. of the type described which positively and quickly extinguishes an arcv spot.

Another objectis: to provide a device which doesnot require large capacity means or mechanical switching.

This invention will be best understood from the following description of an. exemplification thereof, reference being had to the accompanying drawings, wherein:

Fig. 1 is-a cross-sectional view of one embodiment of the invention;

Fig. 2 is a cross-section on line 2-2 of Fig. 1;

Fig. 3 is a partial cross-section on line 3-3 of Fi 1;

Fig. 4 is. a diagrammatic representation of a system with which the invention may be practiced;

Fig. 5 is a cross-section of the electromagnet adjacent the main envelope on line 5-5 of Fig. 1;

Fig. 6 is a greatlyenlarged partial cross-sec-tion of Fig. 3 detailing the magnetic field; and

Fig. 7 is a. simplified graph representing certain operational conditions of the invention.

Referring now more particularly to Fig. 1, the device comprises a substantially cylindrical vitreous envelope I having integral with the lowermost portion thereof and perpendicular to its axis a vitreous tubular member H closed at the free end thereof, the opposite end opening into said main envelope l1). Supported within said envelope by an electrically conductive member 12 embedded in said envelope is an anode l3, preferablyof carbon. A resistance igniting electrode i4 supported within said enevlope by an electrically conductive member l has its pointed portion partially immersed in the mercury liquid pool cathode l6.

Supported within tubular member I l 'is an auxiliary electrode ll, said electrode being composedof carbon, for example, and supported by electrically conductive members l8 embedded in said envelope H. Between said electrode 1'! and closed end IQ of tubular member H, and transversely positioned therein, is a perforate member 20. As illustrated in Fig. 2, said perforate member comprises a frame 2| ofnon-magnetic material such as non-magnetic steel or the like. Inserted within a substantially rectangular opening in said frame is a plurality of slugs or bars 22 of magnetic material, which may be iron for example. The spaces between bars 22 are made sufficiently wide so that capillary action of the mercury cathode between said bars. does not interfere with the flow thereof and same can flow readily in the interstices. of. perforate member 20. However, it is possible to use nickel which is also magnetic and has the advantage that it can be wetted by the mercury cathode. Using nickel as. the material for bars 22 allows closer spacing. The capillary action when the liquid can wet the grid bars permits the liquid to readily enter a confined space. The narrower spacing soprovided-steps up the efiiciency of the extinguishing feature of the perforate member as the arc spot would be broken up in the narrower interstices of the perforate member and more readily extinguished. Perforate member 20 is supported within the tubular member by electrically conductive members 28A, said conducting members being-embedded in sealed end IQ of tubular member ll.

Adjacent electrode I1 is placed an electromagnet 24, the field of which is in the plane of the surface of cathode IB, said electromagnet having two windings 25, 26 surrounding the two legs or poles 21, 28 as delineated in Fig. 5, the axis of the extended portions 29, 30 of said legs 21, 28being transverse of the axis of said tubular member l I. Both windings 25, 26 are wound in a direction which would make legs 21, 28 south poles when said windings are energized as explained hereinafter. Positioned adjacent perforate member 20 is a permanent magnet 3| forming a partial yoke around the tubular member I l, the axis of the field of said magnet 3| being at right angles to the vertical axis of said perforate member 20 so as to set up intense magnetic fields in spaces 22A between bars 22.

In connection with the foregoing paragraph, the eifectiveness of magnet means 3| for inducing an intense field in the interstices 22A of the perforate member 21 will be discussed. The field thus induced in said interstices presents an arcuate front 44 to oncoming are spot 45. Re-

;gardless of directions of path of the are spot 45 toward the perforate member, when said spot enters the arcuate shaped field 44 it tends to travel, due to. the eifect inherent in retrograde motion of an arc spot in a magnetic fieldyalong a path 46 in a' direction normal to'a tangent to said field 44 and is thus very efiectively drawn into the interstices 22A. Entry'of the arc-spot 45 into narrow interstices 22A causes abrupt extinction of said spot as the ions are rapidly diffused to the walls of bars 22. Because deionization proceeds at a rate greatly in excess of ionization it becomes impossible to sustain the arc discharge. Rapid diffusion of the ions is due to the very narrow spacing 22A of the perforate member 20.

Fig. 31s a cross-section of the tubular member taken longitudinally of said member and illustratesclearly the arrangement of non-magnetic metal deflecting members 23. As indicated these members are aflixed to frame 2| of perforate member 20 and the free ends of said deflecting members diverge toward the walls of tubular member II in a direction toward the opening in main envelope l0. As the are spot or spots, as the case may be, race into tubular member I l with a retrograde motion toward the perforate member, said are spot or spots are guided into the interstices 22A of the perforate member with greater efficiency.

Retrograde motion is defined herein as the direction taken by an are spot which is opposite to the electromagnetic push, the path an arc spot takes being along a line at right angles to the axis of said field. This retrograde motion is contrary to the usually understood behavior of an arc in a transverse field, said are usually being considered as going in the direction of the forces applied to the ionized region. Furthermore, although the arc cathode spot races along the cathode surface in a retrograde direction, the mercury vapor from the are spot moves away from the are spot in a direction opposite the motion of the are spot. The vapor therefore behaves as usually understood in a transverse magnetic field. Were this phenomenon not so and the vapor preceded the arc spot, said spot would never reach perforate member 20 and extinction could not take place. The motion of the vapor upon reaching the perforate member would be impeded and-inasmuch as said spot is carried along by the'vapor it would also stop.

Retrograde motion of an are spot in the transverse magnetic field occurs at pressures below about 3 mm. of Hg for practically all spacings of anode and cathode, provided the magnetic field is between zero and 5000 gauss. If anode spacing and magnetic field strength are maintained constant while the pressure of the conducting gas or vapor is increased, there will be found a critical pressure at which retrograde motion ceases. Above this critical pressure, ordinary motion takes place.

To'continue retrograde motion of the are spot above the critical pressure herebefore mentioned, spacing of main electrodes l3 and I6 is decreased below the critical value of electrode spacing above recited. As illustrated in the graph of Fig. 7 in which P represents the pressures above the critical Value hereinbefore recited and l/d the reciprocal of the space below the criticalvalue mentioned above, values above curve A, B will cause a reversal of retrograde motion of the arcspot and values below said curve will produce retrograde motion. Therefore, with spacing of the main electrodes i 3 and I6 less than the critical value herein recited and a field within the critical range mentioned, pressure times the distance at which retrodgrade motion ceases is approximately a constant.

Fig. 4 is a diagrammatic representation of the device when practiced in connection with a resistance welding circuit. Battery 33 or other source of potential is connected to igniting electrode M. In series with said battery is starting switch 34 which when operated impresses a potential impulse on igniting electrode l4 and causes an incipient arc cathode spot to appear on the surface of cathode'lfi. Anode I 3 has a potential impressed on it from direct current input 35, through current limitin resistor 36, primary winding 31 of welding transformer 38, and winding 26 on electromagnetic pole 28. Auxiliary electrode I1 is impressed with a potential from D. C. source 35 through current limiting resistor 39. Said last-named electrode l1 serves to pick up the main discharge between the anode l3 and the cathode l6 when the arc cathode spot is caused to move, under said electrode H, in a direction toward the erforate member 20 and so functions to guide the cathode spot along a predetermined path. Potential to energize winding 25 on electromagnetic pole 21 is received from battery '40 or some other source of potential. Condenser 4| is shunted across series connected windings 26 and 31 and serves to cushion the electromotive force of the welding system when the current is interrupted.

Having described in idetail the various structural components of the present device, the mode of operation of said device when practiced in connection with a welding circuit will be discussed.

Assume that the device is in a non-conducting state and pole 21 of the electromagnet 24 has induced therein a field through the medium of winding 25, said winding being energized by battery 40. As pointed out heretofore, winding 25 is wound in a direction so as to induce in said pole 21 a magnetic field which makes said pole a south pole. The field intensity of said pole '21 is about 5000 gauss, more or less.

Manipulating switch 34 impresses a potential impulse from battery 33 on igniting electrode 14 whereupon an incipient arc cathode spot is formed on the surface of cathode I6, and as soon as sufficient ionization takes placebetween these last-named electrodes, the discharge will begin to pass to anode l3, conduction will start and anarc spot capable of sustaining the discharge will be formed.

Immediately previous to the conduction period just recited, the magnetic field of pole 21, which is in the plane of the surface of cathode I6 and adjacent the opening HA of the main envelope I0, confines the are spot to a region substantially within the area where said spot is initiated. Were it not for this particular feature of the present device, the are spot would start racing along the surface of the cathode into tubular member ll toward perforate member 20. In order to control the extinguishing period of the device, the magnetic field of pole 2'! is momentarily made a barrier to the motion of the are spot. However, as the conduction cycle proceeds and current flows through primary winding 31 and thence through electromagnetic winding 20 on pole 28, a greater field is induced in pole 28 than that which is present in pole 21, and consequently pole 28 is now a south pole, the field reverses its direction in the plane surface of cathode I6 and the are spot has imparted to it a retrograde motion toward perforate member 20. With the impetus given the are spot by the field of electromagnet 24, the are spot races along cathode surface l6, and comes under the infiuence oi the field of magnet 3| and into the interstices 22A of perforate member 20. The field of magnet 3| may be of the order of about 5000 gauss or less. The are spot upon entering said interstices 22A is abruptly'extinguished.

Upon extinction of the are spot, the current is quickly interrupted, causing a collapse of the field in winding 31 of transformer 38, a transfer of energy to th secondary 42 and a flow of current through the work 43. The cycle is again repeated when desired. The actual operation of resistance welding circuits being Well known to those versed in th art, no attempt is made to discuss the details pertaining to the equipment involved in such operation.

The are spot on a mercury pool is of the highly mobile type which moves rapidly over the surface of the cathode. This same type of are spot can be initiated on other materials, such as copper, aluminum and the like. Such highly mobile types of are spot on these materials perform along the same principles with respect to retrograde motion as described above in connection with mercury pool cathodes.

Having described and illustrated the present invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

What is claimed is:

1. An arc discharge device comprising: an envelope having an auxiliary portion extending substantially perpendicular to the axis thereof; an anode supported within said envelope; a liquid cathode disposed within said envelope; means for initiating an arc spot on the surface of said cathode; a perforate member disposed within the auxiliary portion of said envelope, parallel to the axis and perpendicular to the surface of said cathode; magnetic means disposed adjacent said perforate member; and means for energizing said magnetic means to urge said are spot into the interstices of said perforate member, said perforate member having induced in the interstices thereof a magnetic field of sufficient magnitude to extinguish said are spot.

2. An arc discharge device comprising: an envelope having an auxiliary portion extending substantially perpendicular to the axis thereof; an anode supported within said envelope; a liquid cathode disposed within said envelope; means for initiating an are spot on the surface of said cathode; a perforate member disposed within the auxiliary portion of said envelope; said perforate member being parallel to the axis and perpendicular to the surface of said cathode, and partly immersed in said cathode, said perforate member consisting of a plurality of spaced parallel bars; magnetic means disposed adjacent said perforate member; and means for energizing said magnetic means to urge said are spot into the interstices of said perforate member to extinguish said are spot,

3. An arc discharge device comprising: an envelope having an auxiliary portion extending substantially perpendicular to the axis thereof; an anode supported within said envelope; a liquid cathode disposed Within said envelope; means for initiating an are spot on the surface of said cathode; a perforate member disposed within the auxiliary portion of said envelope, parallel to the axis and perpendicular to the surface of said cathode; said perforate member consisting of a non-magnetic frame having a plurality of parallel magnetic members set therein, said members being spaced a distance apart suificient to permit the free flow of said cathode material therebetween; magnetic means disposed adjacent said perforate member; and means for energizing said magnetic means to urge said are spot into the interstices of said perforate member to extinguish said are spot.

4. An arc discharge device comprising: an envelope having an auxiliary portion extending substantially perpendicular to the axis thereof; an anode supported within said envelope; a liquid cathode disposed within said envelope; means for initiating an arc spot on the surface of said cathode; a perforate member disposed within the auxiliary portion of said envelope, parallel to the axis and perpendicular to the surface of said cathode; said perforate member being composed of a material capable of being wetted by said cathode to permit the free flow thereof in the interstices of said perforate member; magnetic means disposed adjacent said perforate member; and means for energizing said magnetic means to urge said are spot into the interstices of said perforate member to extinguish said are spot.

5. An arc discharge device comprising: an envelope having an auxiliary portion extending substantially perpendicular to the axis thereof; a liquid cathode disposed within said envelope; an anode supported within said envelope, in spaced relationship to said cathode; an igniting electrode, supported within said envelope adjacent said cathode, for initiating an are spot on the surface of said cathode; means, disposed within the auxiliary portion of said envelope, for establishing a magnetic field in the plane of the surface of said cathode; the polarity and intensity of said field being such as to impart retrograde motion to said arcspot and draw the same into said field; and means, including a perforate member disposed within the auxiliary portion of said envelope and within the path of said magnetic field, for dispersing the ionized atmosphere adjacent said are spot and thereby extinguish the same.

6. An arc discharge device comprising: an envelope having an auxiliary portion extending substantially perpendicular to the axis thereof; a liquid cathode disposed within said envelope; an anode supported within said envelope, in spaced relationship to said cathode; an igniting electrode, supported within said envelope adjacent said cathode, for initiating an arc spot on the surface of said cathode; means, adjacent the region of said cathode in which said are spot is initiated, for establishing a first magnetic field in the plane of the surface of said cathode; the polarity and intensity of said first field initially being such as to repel said arc spot and maintain the same in said region of its initiation; means, disposed within the auxiliary portion of said envelope and spaced from said first-named means on the side of the latter opposite to said region of arc spot initiation, for establishing a second magnetic field in the plane of the surface of said cathode; the polarity and intensity of said second field being such as to be adapted to impart retrograde motion to said are spot and draw the same into said field; means for reversing the polarity of said first magnetic field, thereby to impart retrograde motion to said arc spot and urge the same toward said second-named means; and means, including a perforate member disposed within the auxiliary portion of said envelope and within the path of said second magnetic field, for dispersing the ionized atmosphere adjacent said are spot and thereby extinquish the same.

CHARLES G. SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Ninnber Name Date 1,834,495 Pilon Feb. 2, 1932 2,210,816 Miles Aug. 6, 1940 2,254,722 Aoki Sept. 2, 1941 

